Suction cups are commonly used to mount and secure objects to smooth surfaces such as the surfaces of glass, plastic, formica, glazed tile, metal, etc. The typical suction cup includes a cup body and a stem. The cup body is generally arcuate or circular and defines a concavity. Typically the stem is integrally formed on the body and used as the place of attachment for the object to be supported by the suction cup. At least the body of the suction cup is made of rubber, plastic or other material having sufficiently resilient properties such that when the body is pressed against a smooth surface the volume of concavity is reduced, forcing air to be expelled so that the body forms an air-tight seal against the smooth surface. Atmospheric pressure outside the body retains the suction cup body against the surface. When the air-tight seal is broken, air rushes into the concavity, releasing the suction attachment to the surface and the resilient material of the suction cup body returns to its relaxed condition. The resilient suction cup can be repeatedly reused.
Problems often arise in use of suction cups in that they are difficult to properly position. Once a suction cup is attached to a surface, the suction forces (atmospheric and friction) resist repositioning of the cup. Attachment of the suction cup to an object can also be a problem. Preferably, the attachment should be releasable.
U.S. Pat. No. 2,221,238 to S. L. Johnson discloses a suction cup having normally closed slits in the stem communicating with the concavity of the suction cup body and a C-shaped clamp for connecting an object to the stem. The suction cup is particularly adapted for mounting a vibrating object such as a typewriter to a horizontal surface. The slits operate similarly to a one-way valve. When the suction cup is pressed against a surface (during installation or downward vibration of the object) air pressure developed in the compressed concavity of the suction cup is expelled through the slits, resulting in creation of a vacuum within the cup body. Outside atmospheric pressure acting on the stem tends to keep the slits closed, thus preventing the entrance of air into the cup. When the body is forcefully lifted vertically away from the surface, the C-shaped clamp presses upwardly against the stem, which stretches the walls of the stem, thereby opening the vent slits and permitting air to enter into the cup to relieve the vacuum and release the cup from the supporting surface.
U.S. Pat. No. 2,319,727 to J. E. Duggan discloses a vented suction cup having a valve in the suction cup body. When it is desired to remove the cup structure from the mounting surface, the valve is pulled sufficiently to distort the rubber and open an air passage. Thus, air from the atmosphere may enter the body of the suction cup to destroy the vacuum and release the cup from the mounting surface.
U.S. Pat. No. 4,196,882 to Rognon discloses a double suction cup holder in which two oppositely oriented suction cups are connected by a shared stem. The double suction cup holder can be used to secure objects such as memo pads to a flat surface. A longitudinal air passageway through the stem connects the concavities of the two cups. An opening traverses the passageway and has a valve member rotatably positioned therein. The valve member has inter-communicating longitudinal and diametrical bores. When the valve is turned so that its diametrical bore communicates with the air passageway in the stem, the vacuum in the cups is spoiled, thereby releasing the cups from the two surfaces.